Performance of three different native plant mixtures for extensive green roofs in a humid subtropical climate context

Most of the services and benefits of green roofs are related to the substrate as well as the vegetation layer. Although plant selection should be made on the basis of green roof typology, morphology, and climate conditions, very often, Sedum species only are used worldwide. However, they do not always guarantee the best performances; hence, it is important to investigate different plant species and their performance in different climate contexts. Herein, an experiment was conducted using three plant mixes (i.e., a Sedum mix, a perennial herbaceous mix, and a suffruticose mix), grown in boxes containing two substrates (a volcanic substrate or a recycled crushed brick substrate) and two drainage/storage layers (a preformed layer or a mineral layer), in factorial combination. The Sedum mix showed a high canopy cover, comparable to or even higher than that of the other mixes, particularly when supplemental irrigation was stopped. However, the actual crop coefficient (Kc act) of the herbaceous and suffruticose mixes was often higher than that of the Sedum mix. The results also showed that both the substrate and the drainage/storage layer may improve Kc act values as a consequence of their capacity for stormwater retention.